The invention relates to the butchering of fish and, more particularly, to apparatus and methods for subdividing a fish body into a loin-containing portion and a viscera-containing portion.
In the processing of fish, such as tuna, meat to be processed for human consumption must be separated from undelectable or otherwise inedible portions prior to canning. Among the inedible portions are the viscera, which reside in the visceral cavity extending on the ventral side of the fish from the head to the vent, or anus. It has previously been recognized that the viscera could be largely removed by cutting crosswise through the fish along a straight line running roughly from the vent through the eyes. Such a cut would separate the fish into a first section containing the loin meat and a second head and belly section containing some belly wall meat and the bulk of the viscera, regardless of the size of the fish.
An apparatus for producing such a cut is disclosed in U.S. Pat. No. 3,675,273, issued Jul. 11, 1972, to Frank V. Vidjak. The tuna butchering apparatus described includes a power-driven vertically movable knife urged toward and away from a table upon which a fish is positioned. The fish, lying on its side on the table, is oriented so that the single knife blade cuts downwardly through the fish from one side to the other along a straight line extending approximately from the center of the eye to the vent.
With the Vidjak apparatus, however, there is a tradeoff between the amount of visceral material cut and the amount of intact loin meat left with the loin-containing portion of the fish. The single planar cutting path across the width of the fish is not compatible with the curved cross-sectional pattern of the visceral cavity. Consequently, either too much meat is removed with the viscera or too much of the viscera remains with the loin-containing fish portion. Furthermore, organs such as the kidney and hemal spine, which reside deeper inside the fish close to the backbone, are difficult to remove without cutting through edible loin meat. With thicker lower loin meat left attached to the thin belly wall meat, uniform cooking of the meat from the separated section is difficult. Thus, to ensure that the thicker sections are adequately cooked, the thin belly wall meat will be overcooked and quality decreased.
Other shortcomings with prior art cutters arise from the blades used. Saws, for example, waste meat along the cut as kerf. The chopping blade of the Vadjak apparatus cuts straight in the nature of a shear without reciprocation or other motion normal to blade advancement. Thus, any dull spots, chips, or other imperfections in the blade affect the quality of the cut.
The apparatus, moreover, requires an impulse of force to cut through the fish, especially if the fish is frozen. Because the rounded side of the fish is lying on a flat table, the force of the blade on the other side of a frozen fish may tend to cause the fish body to shift upon impact of the blade. If the fish moves, the cut will deviate from the desired cutting path.
A key concern in tuna canning is that the canned product be free of bones. Tuna fish have many small flat and round bones that extend along each side of the upper belly wall behind the head of the fish. It is preferable that these bones be separated from the loin portion of the fish. As a consequence, any cut made in the fish must avoid cutting through these bones.
Another fish preparation apparatus is described in U.S. Pat. No. 5,299,974, issued Apr. 5, 1994, to Joachim Jahnke. The apparatus produces a double fillet fish product that includes the head and tail. The apparatus performs a two-step cutting process on an unfrozen fish conveyed backward in a swimming position through two sequential cutting tools. A first cutting tool, comprising a pair of parallel, closely spaced knives having clean-out elements attached to the outer sides of the blades, makes incisions in the ventral side of the fish through which the loose viscera are scraped out by the clean-out elements. A second downstream cutting tool is arranged to cut thin, rib-containing portions from the fish. The end product is a generally whole and boneless butterflied fish.
Current trends in the canning of tuna suggest that automated processing will replace at least some formerly and currently manual tasks. To be useful in the long term, a new tuna processing apparatus should be fully automated or readily adaptable to incorporation in an automated process.
For the foregoing reasons, there is a need for an apparatus for subdividing a fish, especially a tuna, into two sections--a first section containing virtually all of the loin meat and a second section containing thin belly wall meat, the viscera, the belly bones, and other generally inedible matter. The apparatus must be capable of holding a fish steady in a controlled orientation to make accurate incisions in the fish body to minimize the amount of thick lower loin meat accompanying the viscera separated from the remaining fish body. The apparatus must avoid cutting through the belly bones, tolerate dull spots or other blade imperfections, and be readily adapted for use in an automated process.